Crimping of detonators

ABSTRACT

A device for crimping the mouth of a detonator housing comprises a pair of opposed jaws reciprocally movable relative to each other, and a plurality of toothed segments on each jaw. The segments are moveable, are located in a jaw cavity, and together form a segmented ring. The side faces of each segment converge from a broad radially outer end towards a toothed radially inner narrow end. A resiliently stressable biasing element is provided between each adjacent pair of segments. The biasing elements act to space the segments of each pair apart when the jaws are spaced apart from each other, and also act to permit the segments, in response to movement of the moveable segments arising from the closing of the jaws, to abut against one another in series when the jaws are tightly in contact with each another, to form the segmented ring.

THIS INVENTION relates, broadly, to the crimping of detonators for detonating explosives. More specifically, the invention relates to a device and a method for crimping the mouth of a metal detonator housing around an initiating element such as a shock-tube, fuse or electrical lead protruding into the housing.

According to the invention, there is provided a device for crimping the mouth of a metal detonator housing around an initiating element protruding into the housing through the mouth, the device comprising

-   -   a pair of opposed jaws, at least one which is movable relative         to the other and is reciprocally mounted so that at least one of         the jaws is reciprocally movable alternately towards and away         from the other jaw to successively bring the jaws tightly into         contact with each other and then to space the jaws apart from         each other;     -   a plurality of toothed segments arranged side-by-side in series         on each jaw, at least some of the segments being moveable and at         least some of the segments of each jaw being located in one or         more cavities provided therefor in the jaw, each segment having         a pair of side faces whereby the segment abuts an adjacent         segment when the jaws are tightly in contact with each other so         that the segments of the jaws together form a segmented ring,         the side faces of each segment converging from a broad radially         outer end of the segment towards a toothed radially inner narrow         end of the segment, each segment thereby having a tapering shape         when viewed in a direction parallel to the axis of the ring,         with the teeth of each segment being parallel to said axis;     -   a resiliently stressable biasing element provided between each         adjacent pair of segments in a jaw, the biasing element acting         to space the segments of the pair apart when the jaws are spaced         apart from each other and acting to permit the segments, in         response to movement of the moveable segments arising from the         closing of the jaws, to abut against one another in series when         the jaws are tightly in contact with each another, to form the         segmented ring, the ring defining, at its centre, a passage         having a toothed cross-sectional outline provided by the toothed         narrow ends of the segments for holding a crimped mouth of a         detonator, the mouth having been crimped by the toothed inner         ends of the segments in response to radially inward movement of         the segments caused by the tight closing of the jaws.

Each jaw may have the same number of segments. The number of segments in each jaw may be selected by routine experimentation, bearing in mind difficulties in obtaining a desirably circular toothed passage when the jaws are tightly closed, when there are too few segments, and difficulties associated with expense and complexity of construction, when there are too many segments.

The number of segments in each jaw may thus be in the range of 2 to 8, more preferably 3 to 5, and conveniently 3.

More particularly, each jaw may have an odd number of segments, for example 3, 5 or 7, the preferred number again being 3, so that there are, in each jaw, a central segment and one or more additional segments on each side of the central segment.

At least one segment in each jaw, for example the central segment, may be fixed and hence immovably connected or integral with the remainder of its associated jaw, with a cavity being provided in the jaw on each side of the fixed segment for receiving one or more movable segments.

Alternatively, all of the segments may be movable, being in the nature of movable inserts, a single cavity being provided in each jaw for receiving the inserts, in which cavity the inserts are located.

Each cavity may provide one or more abutment faces for abutting respectively against the broad ends of the movable segments. The abutment faces may be flat and the broad ends of the movable segments may have radially outwardly facing surfaces which are also flat. Each abutment face and the radially outer surface of the associated segment may be provided with a radial projection which projects into an associated tangential slot, relative to the ring. The projection may be a radially outward projection from the outer surface of the broad end of the segment and the tangential slot may be provided in the abutment face of the recess, or in principle vice versa, with the projection projecting radially inwardly from the abutment face of the recess and the tangential slot being provided in the outer surface of the broad end of the segment.

When there is an odd number of segments in each jaw, however, there need be no slot and projection acting between the outer surface of the broad end of the central segment and the associated abutment face, the abutment face and outer surface of the central segment instead respectively being provided with opposed sockets, and a biasing member such as a coil spring under axial compression or an elastomeric block under similar axial compression, being located in the opposed sockets and spanning the interface between the outer surface of the broad end of the central segment and the abutment face, the compression of the biasing member acting to urge the outer face of the central segment away from the associated abutment face.

Each biasing element may be an elastomeric block which is held captive in a cavity provided therefor in the side face of one of the segments of the pair of segments between which it acts. The elastomeric block may project tangentially outwardly from its cavity relative to the axis of the ring, when the jaws are spaced apart from each other, the block thereby acting to space apart the segments of the pair, and is compressed and forced into its associated cavity by the side face of the other segment of the pair when the jaws are tightly in contact with each other. Each elastomeric block may be cylindrical in shape, being located in a correspondingly part-cylindrical cavity having an axis which is parallel to the axis of the ring.

Each jaw may comprise a more or less elongated rectangular flattened bar, conveniently of metal, the bar being longer than it is wide and wider than it is thick, so that it has a pair of major faces spanning its length and width, a pair of side edge faces spanning its length and thickness, and a pair of end edge faces spanning its width and thickness, the bars abutting against each other, by means of a pair of opposed side edge faces thereof, when the jaws are in the tightly closed condition. In this case the cavities holding the respective series of segments may be more or less semi-regular-polygonal indentations into the respective opposed side edge faces of the bars, the indentations extending from one major face of the bar to the other. The axes of the polygons may be parallel to the axis of the ring, and each cavity may in turn also extend from one major face of the bar to the other. Each major face of each bar may be enclosed by a cover plate, which acts to hold the segments and biasing elements in place against axial movement thereof in the direction of the ring axis.

The device may include a guide pin protruding from at least one of the segments, into a complementary guide slot in the cover plate which abuts that segment. Typically, each of the segments may be provided with such a guide pin, with each guide pin then located in its own complementary guide slot.

The jaws may further be provided respectively on their side edge faces which abut when the jaws are tightly in abutment, with a guide pin and an opposed tubular guide socket, the pin entering the socket when the jaws approach each other, and leaving the socket when the spacing between the jaws is increased sufficiently, as the jaws leave each other.

In use, a succession of detonator housings are moved intermittently in series along a path extending between the jaws, in a direction perpendicular to the axis of the ring, with their associated initiating elements in place, optionally held there by a resiliently flexible sleeve or ferrule located coaxially between the mouth of the detonator housing and the initiating element, the detonator housings being aligned parallel to the ring axis, while the jaws are spaced apart, with each detonator housing being placed between the jaws and coaxially aligned with the ring axis, before the jaws are moved together into tight abutment with each other to clamp the detonator housing mouth between the jaws by means of the segments, the segments moving radially inwardly towards the ring axis to crimp the mouth of the detonator housing around the initiating element.

The invention accordingly extends to a method of crimping the mouth of a metal detonator housing around an initiating element, the method including the steps of:

-   -   moving a succession of detonator housing in series         intermittently along a path extending between a pair of opposed         jaws, the detonator housings being in turn located in a         stationary condition between the jaws; and     -   moving the jaws into abutment with each other to grip a mouth of         the stationary detonator housing located therebetween by means         of toothed segments mounted on the jaws which, when the jaws are         tightly in abutment with each other, form a segmented ring         defining, at its centre, a passage having a toothed         circumferential outline,

the segments being arranged simultaneously to move radially inwards towards and into contact with the mouth of the housing located between the jaws as the jaws approach each other, to crimp the housing against the initiating element by the time the jaws are in tight abutment with each other, the detonator housing being coaxially aligned with the axis of the ring and the detonator housings being moved in succession, while the jaws are spaced apart, in a direction perpendicular to the ring axis, the jaws being moved apart after the mouth of each detonator housing has been crimped, to allow the succeeding detonator housing to be moved into its stationary condition between the jaws, before the jaws are again moved together to crimp the mouth of said succeeding detonator housing.

In accordance with the method, moving the jaws into abutment may be against a bias which acts to space the segments apart from one another and to space the segments radially outwardly, automatically to enlarge the ring, as the jaws move apart.

It is a feature of the invention that it allows the series of detonator housings intermittently to be moved, typically in a straight line, along a path extending between the jaws and perpendicular to the ring axis, while the jaws are reciprocated in synchronisation with the intermittent movement of the detonator housings, between a tightly abutting condition with their segments located around a crimped detonator housing mouth, and a condition spaced apart to allow subsequent movement of the detonators along the path, thereby permitting low crimping cycle times, as short as about 2 s or less, for the crimping of each detonator housing mouth.

The invention will now be described, by way of non-limiting illustrative examples, with reference to the accompanying diagrammatic drawings, in which:

FIG. 1 shows a sectional plan view of a device in accordance with a first embodiment of the invention, in a direction parallel to the axis of its ring of segments, with its jaws spaced apart;

FIG. 2 shows a view corresponding to FIG. 1, with the jaws tightly in abutment; and

FIG. 3 shows an exploded three-dimensional view from the bottom and side, of a device in accordance with a second embodiment of the invention.

Referring to FIGS. 1 and 2, reference numeral 10 generally designates a device in accordance with a first embodiment of the invention for crimping the mouth of a metal detonator housing (not shown). The device 10 comprises, broadly, a pair of opposed elongate-rectangular hardened mild steel jaws 12, 14, having a length of 120 mm, a width of 40 mm and a thickness of 20 mm. The jaws thus have 120×40 mm² major faces, 120×20 mm² side edge faces designated 16, and 40×10 mm² end edge faces designated 18. In the drawings, the jaws 12, 14 are viewed face-on to their major faces and are shown with their major faces co-planar, one face 16 of the jaw 12 being opposed to one face 16 of the jaw 14, the opposed faces 16 being shown tightly in abutment at 20 in FIG. 2, and spaced apart by a spacing “S” in FIG. 1.

In the present example, the jaws 12, 14 are reciprocably mounted on a hydraulic reciprocating mechanism (not shown) arranged to reciprocate them simultaneously between a closed condition, shown in FIG. 2, and a fully open condition in which they are spaced apart sufficiently to allow a series of detonator housings to be crimped to pass between the jaws in a direction parallel to their edge faces 16. The direction of reciprocation is normal to the faces 16 and is shown by arrow 22, and the direction of movement of the detonator housings is shown by arrow 24.

It is to be noted that in FIG. 1 the jaws 12, 14 are not shown fully spaced apart, but only partly spaced apart, the jaws in their fully spaced-apart condition permitting a succession of detonator housings to pass therebetween in the direction of arrow 24, midway between their opposed side edge faces 16, without being interfered with by the guide pin 26 (described hereunder) provided on the jaw 12. In other examples, the jaws may be movable by a pneumatic reciprocating mechanism or by a mechanical reciprocating mechanism such as a crank; and it will be appreciated that in other examples only one of the jaws 12, 14 need reciprocate, the other being stationary.

In the present example, the detonator housings are carried past the jaws 12, 14 by a conveyor mechanism (not shown) situated below the jaws 12, 14, the edge faces 16, 18 being vertical and the major faces being horizontal, with the detonator housings projecting upwardly from the conveyor mechanism to present their mouths at a desired elevation between the opposed side edge faces 16. The conveyor mechanism moves a succession of detonator housings intermittently in the direction of arrow 24 when the jaws 12, 14 are sufficiently spaced apart, and holds the detonator housings stationary at other times. Only one detonator housing at a time will be located between the opposed jaw faces 16, the spacing between, and/or speed of movement in the direction of arrow 24 of, succeeding detonator housings moved by the conveyor mechanism being selected accordingly; and the movement of the detonator housings in the direction of arrow 24 will be appropriately synchronised with the reciprocation of the jaws 12, 14 so that the detonator housings are moved in the direction of arrow 24 only when the jaws 12, 14 are sufficiently spaced apart, and are held stationary at other times, particularly when interference with detonator housing movement by the pin 26 arising from too close a spacing between the jaws 12, 14 is possible.

As shown in the drawings, the pin 26 is held captive in a passage 28 in the jaw 12, by a screw 30 which screws axially into the inner end of the pin 26 and engages with a tapped extension 32 of the passage 28. The jaw 14 is in turn provided with a passage 34 which receives the part of the pin 26 which projects from the jaw 12, when the jaws 12, 14 are sufficiently closely spaced from each other, to guide accurate movement of the jaws into face-to-face abutment of their side edge faces 16.

Each jaw 12, 14 is provided, in its side edge face 16 which faces the other jaw, with a semi-regular-hexagonal indentation 36 (see FIG. 1 in particular) which is broadly C-shaped and provides three abutment faces 38, namely a central abutment face and a pair of lateral abutment faces respectively on opposite sides of the central abutment face. The faces 38 are flat and are directed radially inwardly towards the axis 40 of the hexagon of which they form part. Each of the lateral abutment faces 38 is provided with a slot 42. Each slot 42 is located midway between the major faces of the associated jaw 12, 14 and extends in a tangential direction relative to the associated axis 40. Each central abutment face is provided with a centrally positioned passage 44 which receives a sleeve 46 as described hereunder (see FIG. 2).

Three hardened mild steel segments 48 are provided in each indentation 36, namely a central segment and a pair of lateral segments on opposite sides of the central segment. Each segment 48, when viewed in a direction parallel to the axes 40, is broadly equilateral-triangular in outline, having a broad end 49 which is radially outermost, for abutment against an associated abutment face 38, a pair of side faces 51 for abutment against adjacent segments 48, and a toothed inner narrow end 53, having teeth which extend parallel to the axes 40, the abutment in question taking place when the jaws 12, 14 are in abutment, as shown in FIG. 2. The broad ends 49 of the lateral segments 48 remain at all times, however, in abutment with the lateral abutment faces 38 having the slots 42.

Each of the lateral segments 48 has an insert 50 screwed into a tapped socket in the broad end 49 of the segment 48, the insert 50 providing a projection which projects radially outwardly, relative to the associated axis 40, from the broad end of the segment 48, into the associated slot 42 in the associated abutment face 38. Location of this projection in the associated slot 42 holds the lateral segments 48 captive in the associated indentation 36, the lateral segments in turn holding the respective central segments 48 captive in said indentations 36. One side face of each segment 48 is provided with a part-cylindrical cavity 52 which holds a cylindrical rubber biassing element in the form of a cylindrical block 54 press-fitted into the cavity 52.

As shown in FIG. 1, each sleeve 46 contains a coil spring 56 under compression, each sleeve 46 projecting into a socket 58 provided therefor in the central segment 48 associated with the central abutment face 38 having the passage 44 receiving said sleeve 46. Each sleeve 46 thus projects from the socket 58 in the associated central segment 58, into the associated passage 44 in the associated abutment face 38, being a press fit in the socket 58, but being slidable in the passage 44. The coil spring 56 acts against segment 48 at the inner end of the socket 58, and against a plug 60 held in an extension of the passage 44 by a grub screw 62. The springs 56 are omitted from FIG. 2 for ease of illustration.

Two plastics cover plates are provided to cover the major faces respectively of each jaw 12, 14. Minor projections of the lower cover plate can be seen in FIG. 1 at 64. The cover plates are bolted to the jaws 12, 14 by bolts 66 provided with washers 68, the positions of the bolts 66 and washers 68 being illustrated schematically. The cover plates act to enclose the segments 48 to prevent unwanted movement of the rubber blocks 54 and the segments 48 in the direction of axes 40, while protecting against the ingress of dirt.

It will be appreciated that, when the opposed faces 16 of jaws 12, 14 are in tight abutment at 20 as shown in FIG. 2, the broad end 49 of each central segment 48 abuts its associated abutment face 38, the side faces 51 of adjacent pairs of the segments 48 all being in abutment and the rubber blocks 54 all being under lateral compression and forced laterally into their respective cavities 52. The axes 40 will coincide and the segments 48 will form a segmented ring around a central axis, also designated 40 in FIG. 2, provided by the coinciding axes 40 of FIG. 1. When the opposed abutting faces 16 of the jaws 12, 14 move apart, the springs 56 push the central segments away from their respective abutment faces 38, and the rubber blocks 54 push adjacent pairs of segments 48 apart, as shown in FIG. 1. It will be appreciated that, in FIG. 2, the ring of toothed radially inner narrow ends 53 of the segments 48 combine to form a central passage around the central axis 40, their teeth being parallel to said axis 40.

In use, as mentioned above, the conveyor mechanism, when the jaws 12, 14 are sufficiently spaced apart, successively and intermittently moves the detonator housings into position, in the direction of arrow 24, to place them at the position of the central axis 40 shown in FIG. 2, with the projections of the inserts 50 being located at the ends of their respective slots 42 which are closest to the opposed edge faces 16 of the jaws 12, 14, and with the rubber blocks 54 spacing the side faces of the segments 48 apart. When the jaws are moved together, with the detonating housing held stationary and coaxial with the central axis 40, engagement of the lateral segments 48 of the jaw 12 with the lateral segments 48 of the jaw 14, via the two rubber blocks projecting into the space “S” between the jaws 12, 14, compresses the various rubber blocks 54 and forces them into the associated cavities 52, while bringing the side faces of the segments 48 into abutment. Simultaneously therewith, the springs 56 are compressed to bring the broad ends of the central segments 48 into abutment with their associated abutment faces 38; and the lateral segments 48 slide along their respective abutment faces 38 until the projections of their inserts 50 are at the ends of their associated slots 42 furthest from the opposed faces 16 of the jaws 12, 14, at which stage the situation shown in FIG. 2 is reached, with the opposed faces 16 in abutment.

It will be appreciated that, as the jaws 12, 14 move together, as described above, the toothed radially inner narrow ends of the segments 48 converge axially inwardly towards the axis 40 and towards one another, until they form the substantially circular central passage shown around the central axis 40 in FIG. 2. When they reach the mouth of the detonator housing located coaxially with the central axis 40, said toothed radially inner ends act to crimp the mouth of the housing around the initiating element (and any sleeve or ferrule holding the initiating element) projecting in the housing. When the jaws 12, 14 are subsequently moved apart, the rubber blocks 54 act automatically to space the side faces of the segments 48 apart in each jaw 12, 14, while the springs 56 automatically move the central segments 48 away from their respective abutment faces 38, the projections of the inserts 50 of the lateral segments 48 moving back to the ends of the associated slots 42 closest to the opposed faces 16 of the jaws 12, 14, the outer ends of the lateral segments 48 sliding along their respective abutment faces 38.

Referring to FIG. 3, reference numeral 100 generally designates a device in accordance with a second embodiment of the invention, for crimping the mouth of a metal detonator housing (not shown).

Parts of the device 100 which are the same as, or similar to, those of the device 10 of FIGS. 1 and 2, are indicated with the same reference numerals.

In the device 100, the pin 26 in the jaw 12 and the complementary passage 34 in the jaw 14, have been dispensed with.

The device 100 includes upper cover plates 102, 104 and lower cover plates 106, 108. Bolts 66 protrude inwardly from the lower cover plates 104, 108, through passages 110 in the jaws 12, 14, and engage threaded sleeves 112 protruding inwardly from the upper cover plates 102, 104.

The device 100 also includes a guide pin 114 protruding from each of the segments 48, with each guide pin nestling or located movingly in a guide slot 116 provided in one of the lower cover plates 106, 108. The guide pins 114 and guide slots 116 ensure accurate and consistent movement of the segments 48.

It is a feature of the invention that the simple reciprocating movement of the jaws 12, 14 (arrow 22), and the simple intermittent movement of the detonator housings along their path between the jaws 12, 14 (arrow 24) allow rapid cycle times for the crimping of individual detonator housing mouths, expected to be of the order of 2 s or less.

Finally, it is to be noted that, although in the examples shown in the drawings the detonators are described as moving in the direction of arrow 24, in other examples they can move in a direction perpendicular or normal to the direction of arrow 24, and parallel to the direction of arrow 22. In this case the jaws 12, 14 will not only be reciprocated towards and away from each other in the direction of arrow 22, but will also be indexed simultaneously in a direction parallel to the direction of arrow 24 into crimping stations in which they can reciprocate towards and away from each other, and out of said crimping stations in a direction parallel to the direction of arrow 24, to allow subsequent movement of the series of detonators, in a direction parallel to the direction of arrow 22. 

1. A device for crimping the mouth of a metal detonator housing around an initiating element protruding into the housing through the mouth, the device comprising a pair of opposed jaws, at least one which is movable relative to the other and is reciprocally mounted so that at least one of the jaws is reciprocally movable alternately towards and away from the other jaw to successively bring the jaws tightly into contact with each other and then to space the jaws apart from each other each jaw being provided with three toothed segments arranged side-by-side in series on each jaw, all of the segments being movable and being in the form of movable inserts located in a single cavity provided in each jaw for receiving the inserts, each segment having a pair of side faces whereby the segment abuts an adjacent segment when the jaws are tightly in contact with each other so that the segments of the jaws together form a segmented ring, the side faces of each segment converging from a broad radially outer end of the segment towards a toothed radially inner narrow end of the segment, each segment thereby having a tapering shape when viewed in a direction parallel to the axis of the ring, with the teeth of each segment being parallel to said axis; a resiliently stressable biasing element provided between each adjacent pair of segments in a jaw, the biasing element acting to space the segments of the pair apart when the jaws are spaced apart from each other and acting to permit the segments, in response to movement of the moveable segments arising from the closing of the jaws, to abut against one another in series when the jaws are tightly in contact with each another, to form the segmented ring, the ring defining, at its centre, a passage having a toothed cross-sectional outline provided by the toothed narrow ends of the segments for holding a crimped mouth of a detonator, the mouth having been crimped by the toothed inner ends of the segments in response to radially inward movement of the segments caused by the tight closing of the jaws.
 2. The device according to claim 1, wherein each cavity provides one or more abutment faces for abutting respectively against the broad ends of the movable segments.
 3. The device according to claim 2, wherein the abutment faces are flat and wherein the broad ends of the movable segments have radially outwardly facing surfaces which are also flat.
 4. The device according to claim 2, wherein a radial projection projects radially outwardly from the outer surface of the broad end of the segment into a tangential slot provided in the associated abutment face of the cavity.
 5. The device according to claim 1, wherein each biasing element is an elastomeric block which is held captive in a cavity in the side face of one of the segments of the pair of segments between which it acts.
 6. The device according to claim 5, wherein each elastomeric block projects tangentially outwardly from its cavity relative to the axis of the ring when the jaws are spaced apart from each other, thereby acting to space apart the segments of the pair, and is compressed and forced into its associated cavity by the side face of the other segment of the pair when the jaws are tightly in contact with each other.
 7. The device according to claim 5, wherein each elastomeric block is cylindrical in shape, being located in a correspondingly part-cylindrical cavity having an axis which is parallel to the axis of the ring.
 8. The device according to claim 1, wherein each jaw comprises an elongated rectangular flattened bar, the bar being longer than it is wide and wider than it is thick so that it has a pair of major faces spanning the length and width of the bar; a pair of side edge faces spanning the length and thickness of the bar; and a pair of end edge faces spanning the width and thickness of the bar, the bars abutting against each other by means of a pair of opposed side edge faces thereof, when the jaws are in the tightly closed condition.
 9. The device according to claim 8, wherein the cavities holding the respective series of segments are semi-regular-polygonal indentations in the respective opposed side edge faces of the bars and extend from one major face of the bar to the other.
 10. The device according to claim 9, wherein the axes of the semi-regular-polygonal indentations are parallel to the axis of the ring.
 11. The device according to claim 8, wherein a cover plate encloses the major face of each bar and acts to hold the segments and biasing elements in place against axial movement thereof in a direction parallel to the direction of the ring axis.
 12. The device according to claim 11, which includes a guide pin protruding from each of the segments, with a complementary guide slot in which each of the guide pins is movingly located, being provided in the cover plate.
 13. The device according to claim 8, wherein the jaws are provided respectively on their side edge faces which abut when the jaws are tightly in abutment, with a guide pin and an opposed tubular guide socket, the pin entering the socket when the jaws approach each other and leaving the socket when the spacing between the jaws is increased sufficiently, as the jaws leave each other. 